1. Field of the Invention
The present invention relates to a transparent conductive layered structure comprising a transparent substrate and a transparent two-layered film being composed of a transparent conductive layer and a transparent coat layer being formed in succession on the transparent substrate, which is used in front panels, etc., of display devices such as Braun tubes (CRTs), plasma display panels (PDPs), vacuum fluorescent display (VFDs), liquid crystal displays (LCDs). The present invention particularly relates to a transparent conductive layered structure having the functions of preventing electrostatic charging or shielding an electric field, and preventing reflection, the two-layered film of which has an excellent scratch strength, and with which a reduction in production cost is expected and a method of producing the same, and a transparent coat layer forming coating liquid used in the method of producing the same, and a display device to which the transparent conductive layered structure is applied.
2. Description of the Related Art
Many OA devices have been introduced to the office as a result of office automation (OA) in recent years and an environment in which the entire day work must be done facing the display of OA device is no longer uncommon.
However, when a job is done next to a cathode ray tube (referred to as the above-described Braun tube: CRT) of a computer, etc., as an example of OA equipment, it must be easy to see the display screen in order to prevent visual fatigue, as well as prevent deposition of dust and electric shock induced by the electrostatic charge on the CRT screen, etc. Furthermore, in addition to these requirements, etc., there has recently been concern over the detrimental effects of low-frequency electromagnetic waves generated by CRTs on the human body and there is a demand for CRTs with which there is no leakage to the outside of such electromagnetic waves.
As measures for such prevention of electrostatic charging or prevention of leakage of electromagnetic waves (electric field shielding), there have been adopted conventionally a method of coating the front panel surface of a CRT, etc., with a transparent conductive layer, and other methods.
Additionally, it is desired that surface resistance of these transparent conductive layers be in the order of 107 to 1011 xcexa9/xe2x96xa1 (ohm per square) for prevention of electrostatic charging and be at least no more than 106 xcexa9/xe2x96xa1 for prevention of leakage of electromagnetic waves, preferably no more than 5xc3x97103 xcexa9/xe2x96xa1, and more preferably no more than 103 xcexa9/xe2x96xa1.
Therefore, several suggestions have been made thus far for meeting these requirements, but of these, the method wherein a coating liquid for forming a transparent conductive layer prepared by dispersing conductive microparticles in a solvent is applied to the front glass of a CRT and dried, and a coating liquid for forming a transparent coat layer comprising as its main component an inorganic binder such as silica sol, and then baked at a temperature of the order of 200xc2x0 C. is known as a method with which low cost and low surface resistance can be realized.
This method that uses a coating liquid for forming a transparent conductive layer is very simple when compared to other methods of forming transparent conductive layers, such as vacuum evaporation and sputtering, has a low production cost, and is a very useful method.
Moreover, for the above-mentioned transparent microparticles, there are used transparent conductive oxide microparticles such as tin antimony oxide (ATO) or indium tin oxide or metal microparticles, etc. For example, in the case of application of ATO, because surface resistance of the film that is obtained is in the order of 107 to 1010 xcexa9/xe2x96xa1, the film is used for preventing electrostatic charging.
In addition, although a coating liquid for forming a transparent conductive layer employing indium tin oxide is used for shielding an electric field, surface resistance of the film that is obtained is in the order of 104 to 106 xcexa9/xe2x96xa1, which is insufficient to block leakage of an electric field therefore a corrective circuit for canceling the electric field is needed.
On the other hand, when compared to coating liquids that use ITO, a film with somewhat lower transmittance, but also low resistance of 102 to 103 xcexa9/xe2x96xa1, is obtained with coating liquids for forming transparent conductive layers that use metal maicroparticles for the above-mentioned conductive microparticles so that shielding an electric field can be performed without use of the above-mentioned corrective circuit.
Moreover, the metal microparticles that are used in the above-mentioned coating liquid for forming the above-mentioned transparent conductive layer are limited to noble metals, such as sliver, gold, platinum, rhodium, palladium, etc., that rarely oxidize in air, as shown in Japanese Patent Applications Laid-Open No. H 8-77832 and Laid-Open No. H 9-55175. This is because if microparticles of a metal other than a noble metal, such as iron, nickel, cobalt, etc., are used an oxide film is invariably formed on the surface of such metal microparticles in an air atmosphere and good conductivity cannot be obtained as a transparent conductive layer.
Moreover, on the other hand, in order to make the display screen easy to see, anti-glare treatment is performed on the face panel surface to prevent reflection on the screen. This anti glare treatment is performed by the method whereby fine irregularities are made in the surface in order to increase diffused reflection at the surface, but it cannot be said that this method is a very desirable method because when used, resolution decreases and picture quality drops.
Consequently, it is preferred that antiglare treatment be performed by the interference method whereby the refractive index and film thickness of the transparent film be controlled so that there is destructive interference of the incident light by the reflected light.
A two-layered film structure wherein optical film thickness of film with a high refractive index and film with a low refractive index has been set at xc2xc xcex and xc2xc xcex, or xc2xd xcex and xc2xc xcex, respectively, is usually used in order to obtain this type of low-reflection effect of the interference method, and film consisting of the above-mentioned indium tin oxide (ITO) microparticles is also used as this type of film with a high refractive index.
Furthermore, of the optical constant (n-ik, n: refractive index, i2=xe2x88x921, k: extinction coefficient) of metals, the value of n is small, but the value of k is very large when compared to ITO and therefore, even if a transparent conductive layer consisting of metal microparticles is used, the same anti-reflection activity induced by interference of light as seen with ITO is obtained with the two-layered film structure.
Moreover, in recent years, in addition to the properties such as the above-mentioned good conductivity, low reflectance, etc., this type of transparent conductive layered structure is requested to have the property of improving the contrast of images by adjusting the transmittance to the predetermined range (40 to 75%) lower than 100% in order to make the display screen easier to see. In this case, the mixing of color pigment microparticles, etc., into the above-mentioned coating liquid for forming a transparent conductive layer also has been performed.
In addition to this, as treatment for water resistance, brine resistance or anti-smudge of these transparent conductive layers, several attempts to make the layers water-repellent have been carried out recently.
Such a transparent conductive layered structure having a transparent two-layered film being composed of a transparent conductive layer and a transparent coat layer is produced, as mentioned above, by applying a coating liquid for forming a transparent conductive layer on a transparent substrate, and drying, and applying a coating liquid for a transparent coat layer as its main components silica sol, etc., and then conducting a heat treatment at a temperature of the order of 200xc2x0 C.
Moreover, because the above-mentioned transparent coat layer comprises as its main component silicon oxide, the layer is formed as a film of relatively high strength by heat treatment at a temperature of the order of 200xc2x0 C.
However, depending on the producers or makers of CRTs, there are cases where the above-mentioned heat treatment temperature is performed only under the condition of the order of 160xc2x0 C. because of the limitation of facility aspect, etc., so that the strength of some transparent coating films may be insufficient due to the low temperature heating.
Similarly, for a coating liquid for forming a transparent conductive layer using the above-mentioned noble metal microparticles, the coating strength of some transparent two-layered films that are obtained is insufficient. It is considered that this is because when compared to conductive oxide microparticles such as ITO, etc., noble metal microparticles are chemically inert, and thus the binding between noble metal microparticles and an inorganic binder matrix is not so strong, and therefore the coating strength of the transparent two-layered films decreases.
The present invention focuses on such problems, its object being to present a transparent conductive layered structure having the functions of preventing electrostatic charging or shielding an electric field, and preventing reflection, the two-layered film of which has an excellent scratch strength (namely coating strength), and with which a reduction in production cost is expected and a method of producing the same, and a transparent coat layer forming coating liquid used in the method of producing the same, and a display device to which the transparent conductive layered structure is applied.
That is, the invention resides in a transparent conductive layered structure, comprising a transparent substrate and a transparent two-layered film being composed of a transparent conductive layer and a transparent coat layer being formed in succession on the transparent substrate,
wherein the transparent conductive layer comprises, as its main components, conductive microparticles having a mean particle diameter of 1 to 100 nm and a binder matrix of silicon oxide, and wherein the transparent coat layer comprises, as its main component, a binder matrix of silicon oxide including one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms.
The invention resides in a transparent conductive layered structure, wherein the conductive microparticles are transparent conductive oxide microparticles or/and noble metal microparticles.
The invention resides in a transparent conductive layered structure, wherein the transparent conductive oxide microparticles are indium tin oxide or tin antimony oxide.
The invention resides in a transparent conductive layered structure, wherein the noble metal microparticles are any of: noble metal microparticles selected from gold, silver, platinum, palladium, rhodium, and ruthenium: alloy microparticles of these noble metals; or noble metal-coated silver microparticles the surface of which is coated with these noble metals other than silver.
The invention resides in a transparent conductive layered structure, wherein the noble metal-coated silver microparticles are silver microparticles coated with gold or platinum only or a composite of gold and platinum.
Next, the invention relates to the invention defining a method of producing the transparent conductive layered structure.
The invention resides in a method of producing the transparent conductive layered structure, comprising the steps of:
applying on a transparent substrate a transparent conductive layer forming coating liquid comprising, as its main components, a solvent and conductive microparticles having a mean particle diameter of 1 to 100 nm dispersed in the solvent;
then applying a transparent coat layer forming coating liquid comprising, as its main component, an inorganic binder composed of silica sol including an alkyl group containing compound having one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms; and
performing heat treatment.
The invention resides in a method of producing the transparent conductive layered structure, wherein the conductive microparticles are transparent conductive oxide microparticles or/and noble metal microparticles.
The invention resides in a method of producing the transparent conductive layered structure, wherein the transparent conductive oxide microparticles are indium tin oxide or tin antimony oxide.
The invention resides in a method of producing the transparent conductive layered structure, wherein the noble metal microparticles are any of: noble metal microparticles selected from gold, silver, platinum, palladium, rhodium, and ruthenium; alloy microparticles of these noble metals; or noble metal-coated silver microparticles coated with these noble metals other than silver.
The invention resides in a method of producing the transparent conductive layered structure, wherein the noble metal-coated silver microparticles are silver microparticles coated with gold or platinum only or a composite of gold and platinum.
The invention resides in a method of producing the transparent conductive layered structure, wherein the transparent conductive forming coating liquid includes an inorganic binder comprising, as its main component, silica sol.
Further, the invention relates to the invention defining a transparent coat layer forming coating liquid used for the above-mentioned method of producing the transparent conductive layered structure.
That is, the invention resides in a transparent coat layer forming coating liquid used for the method of producing the transparent conductive layered structure, comprising, as its component:
a solvent, an inorganic binder composed of silica sol, and an alkyl group containing compound having one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms;
wherein a mixture ratio of the inorganic binder and the alkyl group containing compound is from 0.1 to 20 parts by weight of the alkyl group containing compound to 100 parts by weight of the inorganic binder.
The invention resides in transparent coat layer forming coating liquid, wherein the alkyl group containing compound is a compound including, in a molecule, a hydrolyzable alkoxysilyl group or a functional group generated by hydrolysis of the hydrolyzable alkoxysilyl group.
Moreover, the invention resides in a display device comprising a main apparatus body and a front panel disposed in front thereof,
wherein the transparent conductive layered structure is incorporated as the front panel with the side of the transparent two-layered film thereof being disposed outside.
The preferred embodiments of the present invention will now be described in detail.
In a transparent conductive layered structure comprising a transparent two-layered film being composed of a transparent conductive layer and a transparent coat layer being formed in succession on a transparent substrate, the present invention is aimed at improving a coating strength, particularly scratch strength of the above-mentioned transparent two-layered film. That is, when observed microscopically, on the surface of the above-mentioned transparent two-layered film, there exist fine irregularities, which are one of the factors decreasing the scratch strength.
Here, a scratch strength is literally an abrasion resistant strength which can be evaluated, for example, by a steel wool test, a pencil strength test, a diamond scratch test, etc.
In addition, the present invention was completed based on the discovery that with regard to the above-mentioned transparent coat layer, when this is made of a binder matrix of silicon oxide including a long chain alkyl group, the scratch strength of the transparent two-layered film can be remarkably improved. That is, a long chain alkyl group has such high hydrophobicity that when a transparent coat layer forming coating liquid is applied and dried, portions thereof are oriented on the outer surface of a transparent coat layer comprising as its main component silicon oxide, and therefore the action of the oriented long chain alkyl group can make lubricity of the coating higher. Moreover, it is considered that because the lubricity of the coating becomes higher, the scratch strength can be improved even if there exist fine irregularities on the surface of the transparent coat layer. Furthermore, the layer can also be repellent to water due to the above-mentioned orientation of the hydrophobic long chain alkyl group on the outer surface of the layer.
Here, the above-mentioned long chain alkyl groups should contain 7 to 30 carbon atoms. When carbon atoms are less than 7, there will be a small amount of orientation on the surface, and in addition, even if the long chain alkyl groups are oriented, lubrication action itself that the long chain alkyl groups have will be insufficient and the effect of improving the scratch strength will be small, which will be impractical. In addition, when carbon atoms are more than 30, it might cause a problem in solubility of the alkyl group containing compound having the long chain alkyl groups to the transparent coat layer forming coating liquid or in coatability of the transparent coat layer forming coating liquid, which will not be preferred.
Furthermore, when the above-mentioned alkyl group containing compound has, in a molecule, a hydrolyzable alkoxysilyl group or a functional group generated by hydrolysis of the hydrolyzable alkoxysilyl group [xe2x80x94SiR1x(OR2)y, R1 and R2: CnH2nxe2x88x921, n=0 to 4. X=0 to 2, Y=3xe2x88x92X], the above-mentioned hydrolyzed alkoxysilyl group will be strongly bound to silica, and therefore the binding between the long chain alkyl group portions oriented on the surface of the transparent coat layer and the binder matrix of silicon oxide will be strong.
For example, in the following Comparative Example 1, pencil hardness of the transparent two-layered film comprising gold-silver binary system microparticles and a silicon oxide binder matrix is 6H, on the other hand, in the case of the transparent two-layered film in Example 1 employing the binder matrix of silicon oxide including an n-decyl group (C10H21xe2x80x94) and a trimethylsilyl group [xe2x80x94Si(OCH3)3] (actually, a group [xe2x80x94Si(OH)3] hydrolyzed in the transparent coat layer forming coating liquid occurs), the pencil hardness of 8H results, which represents an excellent scratch strength.
Here, in a transparent coat layer forming coating liquid, a mixture ratio of an alkyl group containing compound having one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms is preferably from 0.1 to 20 parts by weight of the alkyl group containing compound to 100 parts by weight of the inorganic binder (SiO2) in a silica sol, and more preferably from 0.3 to 10 parts by weight. When the above-mentioned alkyl group containing compound is less than 0.1 parts by weight, the effect of the above-mentioned long chain alkyl group will be insufficient, and when it is more than 20 parts by weight, the strength of the binder matrix itself will decrease, which will be unpreferred.
Furthermore, the above-mentioned conductive microparticles of the present invention should have a mean particle diameter of 1 to 100 nm (claim 1). When it is less than 1 nm, it will be difficult to produce these microparticles, and if mean particle diameter exceeds 100 nm, scattering of visible light ray on the formed transparent conductive layer will be so much enhanced that haze value of the film will be too high, which will be impractical.
In addition, the mean particle diameter as used here means the mean particle diameter of microparticles observed under a transmission electron microscope (TEM).
Moreover, for the above-mentioned conductive microparticles included in the transparent conductive layer forming coating liquid of the present invention, transparent conductive oxide microparticles or/and noble metal microparticles is used (claims 2 and 7), and for the above-mentioned transparent conductive oxide microparticles, indium tin oxide or tin antimony oxide can be used (claims 3 and 8), and for the above-mentioned noble metal microparticles, any of: noble metal microparticles selected from gold, silver, platinum, palladium, rhodium, and ruthenium; alloy microparticles of these noble metals; or noble metal-coated silver microparticles the surface of which is coated with these noble metals other than silver can be used (claims 4 and 9).
Here, when specific resistance of silver, gold, platinum, rhodium, palladium, ruthenium etc. is compared, the specific resistance of platinum, rhodium, palladium, and ruthenium is 10.6, 5.1, 10.8, and 6.71 xcexcxcexa9xc2x7cm respectively, which is higher than that of silver and gold being 1.62 and 2.2 xcexcxcexa9xc2x7cm respectively, and therefore use of silver microparticles or gold microparticles is considered to be advantageous in order to form a transparent conductive layer having low surface resistances.
However, when silver microparticles are used, the application will be limited from the aspect of weather resistance wherein degradation by brine or sulfurization is vigorous. On the other hand, when gold microparticles are used, there will be no problem with the above-mentioned weather resistance, but when aspect of cost taken into consideration, the gold microparticles will not always be most preferable.
Accordingly, microparticles wherein on the surface of silver microparticles are coated noble metals other than silver, can be used. For example, the present inventors have already proposed a transparent conductive layer forming coating liquid using noble metal-coated silver microparticles having a mean particle diameter of 1 to 100 nm coated with gold or platinum only or a composite of gold and platinum (claims 5 and 10) and the method of producing the same (refer to Japanese Patent Application Laid-open No. H 11-228872 and the specification of Japanese Patent Application No. H 11-366343).
In addition, for the above-mentioned noble metal-coated silver microparticles, specific resistance of platinum is somewhat higher than that of silver and gold, as previously mentioned, and therefore, as surface resistance of a transparent conductive film. Agxe2x80x94Au system is more preferable than Agxe2x80x94Pt system and Agxe2x80x94Auxe2x80x94Pt system. However, since gold or platinum only or a composite of gold and platinum is used as coating layer on the surface of the above-mentioned sliver microparticles, the good electrical conductivity of the silver is not lost to such an extent that it falls below the level needed for practical application, even if the above-mentioned Agxe2x80x94Pt system or Agxe2x80x94Auxe2x80x94Pt system is used.
Next, for the above-mentioned noble metal-coated silver microparticles, the coating amount of gold or platinum only or a composite of gold and platinum is preferably set within a range no less than 5 parts by weight up to 1900 parts by weight to 100 parts by weight of silver, and more preferably set within a range no less than 100 parts by weight up to 900 parts by weight. When the coating amount of gold or platinum only or a composite of gold and platinum is less than 5 parts by weight, deterioration of the film by the influence of ultraviolet rays, etc., tends to occur, and therefore, no protective effect of the coating will be observed, while when it exceeds 1900 parts by weight, productivity of the noble metal-coated silver microparticles will be down as well as there will be prohibition in terms of cost.
Furthermore, when gold or platinum only or a composite of gold and platinum is coated on the surface of silver microparticles, silver within the noble metal-coated silver microparticles will be protected by the gold or platinum only or the composite of gold and platinum, and therefore, weather resistance, chemical resistance, ultraviolet ray resistance, etc., will be markedly improved.
Next, a transparent conductive layer forming coating liquid employing, as conductive microparticles, noble metal microparticles and transparent conductive oxide microparticles used in the present invention can be produced, for example, by the following methods, respectively.
That is, for a transparent conductive layer forming coating liquid employing noble metal microparticles, a colloidal dispersion of silver microparticles is prepared by a conventional method (for instance, the Carey-Lea method, Am. J. Sci., 37, 47(1889), Am. J. Sci., 38(1889)), and then the silver microparticles are coated with gold by adding to this dispersion a reducing agent such as hydrazine, etc., and an aurate solution are added to this dispersion. A dispersion of noble metal-coated silver microparticles can be obtained in this way. Furthermore, a trace of dispersant may be added to either or both of a colloidal dispersion of silver microparticles and an aurate solution during the gold coating process as needed.
Then, it is preferable to lower the electrolyte concentration in the dispersion using a method, such as dialysis, electrodialysis, ion exchange, ultrafiltration, etc. This is because colloids generally aggregate with electrolytes when the electrolyte concentration is high. This phenomenon is known as the Schulze-Hardy rule.
Finally, a coating liquid comprising noble metal-coated silver microparticles is prepared by accomplishing an adjustment of the components (microparticle content, water content, etc.), etc. by concentration of the colloidal dispersion of noble metal-coated silver microparticles, and addition of an organic solvent, etc.
Moreover, for a transparent conductive layer forming coating liquid employing transparent conductive oxide microparticles, transparent conductive oxide microparticles such as indium tin oxide (ITO) microparticles, antimony tin oxide (ATO) microparticles, etc., and a dispersant are added to a solvent, and then a dispersion of conductive oxide microparticles is obtained by dispersion treatment using a paint shaker, a bead mill, ultrasonic wave, etc. A transparent conductive layer forming coating liquid which contains transparent conductive oxide microparticles can be prepared by accomplishing an adjustment of the components (microparticle content, etc.), etc., by addition of an organic solvent, etc.
By using the transparent conductive layer forming coating liquid having conductive microparticles such as noble metal microparticles, transparent conductive oxide microparticles, etc., as prepared in the above-mentioned manner, the following method can be used to form the above-mentioned transparent two-layered film on a transparent substrate.
That is, a transparent conductive layer forming coating liquid which comprises as its main components a solvent and conductive microparticles having a mean particle diameter of 1 to 100 nm dispersed in the solvent is applied by any method, such as spray coating, spin coating, wire bar coating, doctor blade coating, etc., to a transparent substrate, such as a glass substrate, a plastic substrate, etc., and when necessary, after drying, overcoating with a transparent coat layer forming coating liquid which comprises as its main component silica sol including an alkyl group containing compound having one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms is performed by the above-mentioned method.
Next, after overcoating, heat treatment is performed at a temperature of, for example, the order of 50 to 250xc2x0 C., and the transparent coat layer that was overcoated is cured to form the above-mentioned two-layered film (claim 6).
Improvement of conductivity, improvement of a coating strength, and even further improvement of weather resistance are simultaneously realized here when the transparent coat layer forming coating liquid which comprises as its main component silica sol including the above-mentioned alkyl group containing compound is overcoated by the above-mentioned methods because the silica sol liquid that has been overcoated (this silica sol liquid which includes an alkyl group containing compound having one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms becomes the binder matrix which comprises as its main component silicon oxide including the above-mentioned alkyl group with the above-mentioned heat treatment) soaks into the spaces in the transparent microparticles layer that was formed by pre-application of a transparent conductive layer forming coating liquid which comprises as its main component conductive microparticles and finally the binder matrix is strongly bound to the substrate and the conductive microparticles.
In addition, the reflectance of the transparent two-layered film can be markedly reduced by the above-mentioned transparent two-layered structure film of a transparent coat layer and a transparent conductive layer wherein conductive microparticles are dispersed in a binder matrix.
Furthermore, the optical properties, such as reflectance, transmittance, etc., of the above-mentioned transparent two-layered film even when using a binder matrix of silicon oxide which does not include a long chain alkyl group are still excellent in a similar manner when using a binder matrix of silicon oxide which includes a long chain alkyl group. It is considered that this is because there is little change in optical constant of the binder matrix even when introducing a long chain alkyl group into the binder matrix of silicon oxide.
Here, as this silica sol including an alkyl group containing compound having one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms, there can be used a polymer obtained by adding water and acid catalyst to orthoalkyl silicate and alkyl group containing silicon compounds, such as n-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, n-hexadecyltrimethoxysliane, n-octadecyltrimethoxysilane, n-octadecylmethyldimethoxysilane, n-octadecyltriethoxysilane, etc., for hydrolysis and then promoting dehydropolycondensatlon, or a mixture obtained by adding the above-mentioned alkyl group containing silicon compounds to a polymer (silica sol) obtained by adding water and acid catalyst to a commercial alkyl silicate solution already hydrolyzed and promoted through polymerization up to a tetramer or pentamer, for further hydration and then promoting dehydropolycondensation, etc.
When being added to silica sol, the alkoxysilyl group portions in the above-mentioned alkyl group containing silicon compounds are hydrolyzed within several hours to several days. The above-mentioned transparent coat layer forming coating liquid is preferably used after this hydrolysis. Furthermore, when dehydropolycondensation is promoted, the solution viscosity rises until it finally solidifies and therefore, the degree of dehydropolycondensation is adjusted to the upper viscosity limit with which application to a transparent substrate, such as a glass substrate, plastic substrate, etc., is possible or lower. There are no particular specifications for the degree of dehydropolycondensation as long as it is at the level of the this limit or lower.
Moreover, the alkyl silicate hydrolyzed polymer including the above-mentioned long chain alkyl group forms a cured silicate film (film comprising as its main component a binder matrix of silicon oxide including one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms), with the dehydropolycondensation reaction all but completed, during heating and baking of the transparent two-layered film.
Furthermore, the refractive index of the transparent coat layer can be adjusted to change the reflectance of the transparent two-layered film by adding magnesium fluoride microparticles, alumina sol, titania sol, zirconia sol, etc., to the above-mentioned silica sol including an alkyl group containing compound having one or more types of alkyl groups selected from long chain alkyl groups containing 7 to 30 carbon atoms.
In addition, in the process for forming the above-mentioned transparent conductive layer, the above-mentioned transparent conductive layer forming coating liquid made by mixing a silica sol liquid as the inorganic binder component that makes up the binder matrix in addition to the solvent and the conductive microparticles having a mean particle diameter of 1 to 100 nm dispersed in this solvent may be used (claim 11). In this case also, the same above-mentioned transparent two-layered film is obtained by applying the transparent conductive layer forming coating liquid comprising a silica sol liquid and when necessary, after drying, overcoating a transparent coat layer forming coating liquid by the above-mentioned method.
Furthermore, in the process for forming the above-mentioned transparent conductive layer, the above-mentioned transparent conductive layer forming coating liquid made by mixing a polymer resin in addition to the solvent and the conductive microparticles having a mean particle diameter of 1 to 100 nm dispersed in this solvent may be used. When a polymer resin is added, conductive microparticles in the transparent conductive layer forming coating liquid can be stabilized and longer pot life of the transparent conductive layer forming coating liquid can be obtained. However, since strength and weather resistance of the transparent conductive film that is obtained tend to be somewhat lower, attention should be given when employing the polymer resin.
Moreover, in order to make the display screen easier to see by adjusting the transmittance of the above-mentioned transparent two-layered film to the predetermined range (40 to 75%) lower than 100%, color pigment microparticles, etc., may be mixed into the above-mentioned transparent conductive layer forming coating liquid. For example, one or more types of microparticles selected from carbon, titanium black, titanium nitride, composite oxide pigment, cobalt violet, molybdenum orange, ultramarine, Prussian blue, quinacridone pigment, anthraquinone pigment, perylene pigment, isoindolinone pigment, azo pigment, and phthalocyanine pigment, etc., can be used as the above-mentioned color pigment microparticles.
As described above, a transparent conductive layered structure according to the present invention, as compared to the conventional ones, has an excellent coating strength and weather resistance. Moreover it has an excellent anti-reflection activity and transmission profile, and also has antistatic or electric field-shielding activity. Thus, it can be used, for example, as a front panel, etc., of display devices, such as CRTs, plasma display panels (PDPs), vacuum fluorescent displays (VFDs), field emission displays (FEDS), electroluminescence displays (ELDs), liquid crystal displays (LCDs), etc.